"Gordon Brown needs to tell us the whole truth of why the security of all families in the country has been put at risk."

During a heated prime minister's questions session, Mr Brown told MPs: "I profoundly regret and apologise for the inconvenience and worries that have been caused to millions of families who receive child benefits.

"When mistakes happen in enforcing procedures, we have a duty to do everything we can to protect the public."

He said he had ordered a review by the Cabinet Secretary of data safety in government and would give Information Commissioner Richard Thomas the power to spot check departments to ensure data was safe.

Conservative leader David Cameron said people would "be angry that the government has failed in its first duty to protect the public".

Mr Cameron said people were "desperately worried" and they would "find it frankly weird" that Mr Brown still wanted to go ahead with plans for a national ID cards scheme and register.

Two Labour backbench MPs - Karen Buck and Andy Love - said the government should "pause" and "stand back" from the planned project.

Bank details

The entire child benefit database was sent via internal mail from HMRC in Washington, Tyne and Wear, to the NAO in London via courier TNT on 18 October.

The data on the two missing discs includes names, dates of birth, bank and address details.

CHILD BENEFIT HOAXES

Hours after the blunder emerged, a website claimed to be offering the missing data for download

Fullreleases.com, a site registered in Arizona, lists several files entitled "child benefit", but users must pay $29.95 plus tax to join before they can view them

However, once money is paid the files cannot be accessed and the site appears to be a scam

The HMRC said people should take care with any transaction on the internet and should ring its helpline if they have problems receiving child benefit

Chancellor Alistair Darling said the civil servant had broken the rules by downloading the data to disc and sending it by unrecorded delivery.

Mr Leigh said that a copy he had been given of a briefing note, written by NAO head Sir John Bourn for the chancellor, suggested that senior HMRC officials authorised the release of the sensitive information.

Bosses at the Revenue were not told about the loss of the discs until 8 November, and Mr Darling and Mr Brown learned about the situation on 10 November.

The officials involved waited before informing their superiors in the hope that the discs would be found.

The Metropolitan Police is leading the search for the discs, and the Independent Police Complaints Commission, which oversees the HMRC, is investigating the security breach.

Her Majesty's Revenue and Customs has set up a Child Benefit Helpline on 0845 302 1444 for customers who want more details.

LOST CDS - SEQUENCE OF EVENTS

18 October - Junior official from HMRC in Washington, Tyne and Wear, sends two CDs containing password-protected records to audit office in London through courier TNT, neither recorded nor registered

24 October - When package fails to arrive, second one is sent by registered post and arrives safely

3 November - Senior managers are told first package has been lost

10 November - Prime minister and other ministers are informed

12 November - HMRC tell ministers CDs will probably be found 14 November - When HMRC searches fail, Metropolitan Police are called in

15 November- Richard Thomas, Information Commissioner, says remedial action must be taken before public is informed 20 November - HMRC Chairman Paul Gray resigns; Chancellor Alistair Darling makes announcement to House of Commons